I have talked with World Wide Corals about what PAR levels correspond to what they describe as low, medium and high. This is the answer:
Low 80-150
Medium 151-250
High 250-350
Just remember that flow is as important as light. It can be very difficult to do a mixed reef when you try to get light and flow correct. It can be done, again, it's just difficult.
Other vendors that I have spoken with generally seem to agree with the figures above. LPS do not really need much light at all.